The measurement of disc and shaft displacement has been performed for many years as part of the development, commissioning and monitoring of all classes of turbomachinery. This measurement has traditionally been performed using sensors that cannot operate above the curie point of rare earth magnets. In this paper a programme of work is described that was undertaken to develop a measurement system that could make a measurement of target proximity in a high temperature environment. The specific objectives were to make possible the measurement of turbine disc axial movement and shaft motion in the engine core, close to the combustion chamber or turbine; and secondly to make possible the measurement of tip clearance over shrouded turbine rotors.

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